Diamond-based electrodes are a promising technology for biomedical research. We propose to develop conductive, diamond-based materials as superior electrodes for extracellular, neurological sensing and stimulation. Diamond provides a unique opportunity to integrate stimulation and sensing in the same device. We hypothesize that diamond electrodes will provide real-time neurological sensing capability, with greatly improved sensitivity, selectivity and stability, as well as an expanded potential range of operation over present materials. Diamond may expand neural stimulation capabilities by avoiding side reactions that lead to tissue damage and by providing long-term stability. These advantages will be applicable to a broad variety of neurological systems. These capabilities will be explored through three specific aims focusing on extracellular sensing of dopamine, adenosine, and serotonin and evaluation of neural stimulation, using our diamond technology toward addressing specific neuromodulatory questions. First, we will characterize the electrochemical behavior of a diamond microelectrode with chemically modified surfaces for neurological sensing and neural stimulation capabilities. Second, we will use our characterized diamond electrode to separately measure dopamine, serotonin, and adenosine concentration changes during in vitro neural activity. Each of these applications is opportunity for diamond electrodes to make an immediate impact on understanding neuromodulation in these specific neural circuits. Third, two diamond electrodes will be used to simultaneously stimulate neural activity of single cells and monitor serotonin release in the Aplysia californica. Relevance to Public Health: Diamond is a new tool to aid in our understanding of neurotransmission, and could be incorporated into advanced neuroprosthetic or drug therapy devices. This proposed project should provide the basis of a whole class of robust, implantable diamond-based devices for neurological applications, which could be extended into broader areas of biomedical research.